Thread: help with k value adjustment

hey,
i changed my k value while dyno tuning to overall richen the map to get the tuning as simple as possible. now that im off the dyno i have choosen a k value approximatley 4500 units higher than stock... can i reduce the raw values in my fuel table to essentially remove the additional richenening i added to the map in the 'normal driving' sections?

was trying to find some math but couldnt find it anywhere.

I usually adjust the K-constant to match the A/F reading in the map. So if I'm at 14.7 on the map my a/f is 14.7. I use nistune so I adjust it real time till it's right.

yea, thats what most people usually do. what i did was adjust the k values until WOT was 12.8:1-13.2:1 then fine tuned that... so now the rest of the map is outta sync, rather than wot.
so technically i did it the other way around, so i was wondering just like how we can calculate an estimate for what the k values should be for bigger injectors, can we calculate an estimated raw value for the fuel map with a percentage change in the k value.

This is on quite a few pages - it'll explain what you need to know to get a ballpark value, then fine tuning should be done from there. Check out page 7 specifically, but it is all very useful.

Nissan ECU Tuning Basics

Hey question... Does the ecu understand fuel tables values below 192 (when feedback is on) eg. 188? Or is 192 the minimum fuelling?

bump - I need to know this as well. I'm going to tune open loop (feedback off) when I get my wideband installed this weekend... At idle and cruise - if "0" on the map is about 14.7 (assuming k-value is close to correct), how would I achieve an AFR of something leaner, say, 15.1? Seems like I would need a number less than zero, unless that's where a number below 192 or so comes into play? Help for both of us!

Also, check out this thread for some pointers as far as fuel map values go... it gets the point across, but didn't explain everything I needed to know, might help you better.

blo0d --

The K value alters the injector pulse duration in proportion to the K value itself. In other words, if you double K, you double the duration of the pulse, double the delivery of fuel, and cut the AFR by 50%.

However, the actual values in the fuel map do not work that way. As I tried to explain in the Tuning Saga thread referenced in the post right above this one, the correction factor to the injector pulse width is determined by these equations:

If the MAP VALUE is less than 128, then MULTIPLIER = (DATA + 128)/128
If the MAP VALUE is greater than 128, then MULTIPLIER = (DATA – 64)/128

I have a spreadsheet that I use to calculate these injector duration correction factors for fuel map values with no sweat. We can get to that later.

Both what I have said about K value and Map Value influence on AFR is theoretical. In other words, this is how it ought to work, but it in a real engine you have real physics, real fluids moving at high velocities, and variations that mean you are at best only able to approximate the correct values using these calculations.

So, blo0d, what should you do?

First, I'd like to know how big a change you made in your K value on the dyno. What was the starting value, and what was the ending value. What's the percentage change?

Second, I'd like to know whether you have a wide band O2 sensor that you can use to pull some data on the street. If you do, then I'd be interested to know how the AFR is behaving in the closed loop portions of the fuel map. After a good warm up, what's the AFR at idle? What's the AFR on a level road with constant throttle and speed at 2500 RPM? Do you have the feedback loop turned on in your ECU?

Just for background, what ECU are you using (Calum RT?) And, one last question, this is an NA setup, right? Not turbo?

If you can post some more information, I'll noodle on this a little.

Billc

ECU Tuning this is a very good read too. Helps with all nissan ecu's.